The service life of wooden structures is greatly reduced by biodegradation processes caused by fungal decay such as soft rot, white and brown rot and attack by insects such as damp wood and dry wood termites. It is therefore desirable to treat wooden structures in some way to combat biodegradation to greatly increase their service life.
It has been found that the service life of wooden structures, can be considerably increased if they are inspected regularly and given remedial chemical treatment. Various methods of remedial treatment of wooden structures have been used and include the pouring of treatment liquids such creosote onto the external surface of the wooden structure or the application of bandages containing preservatives. While both of these methods are effective, they have gained only limited acceptance because they are messy and much of the chemical is lost to the environment.
The introduction of diffusible biocides into the interior of a pole should be an effective way of preventing or delaying deterioration but this method has not become a routine procedure because materials and a delivery system which is cost effective are not available.
Australian Patent No. 527,240 discloses the use of a fused monolithic body of boric oxide which dissolves over an extended period into the moisture present in the wood structure to form solution toxic to organisms responsible for decay. As the shaped monolithic bodies are formed by a melt extrusion process in excess of 1000.degree. C., practical processing problems arise and the use of these bodies has consequently not gained wide acceptance, due to their high cost in addition they are extremely slow release and can take many years to fully dissolve even in wood with moisture content in excess of 25%.
U.S. Pat. No. 4,661,157 discloses the use of boron compounds capable of binding with water by hydration to form shaped bodies. The hydration of boron compounds by the method in the above U.S. Patent occurs quickly and results in a product relatively low in density and strength. The above patent suggests the mixing of the boron compounds with various carrier materials to increase the strength but this also has the effect of reducing the relative proportion of active ingredients in the rods and consequently the effectiveness of the shaped bodies.